The following relates to the fastener arts, nuclear reactor arts, nuclear power generation arts, nuclear fuel arts, and related arts.
In environments such as nuclear reactors, ultra-high vacuum (UHV) processing systems, and the like, installed components are not readily accessible. In such environments, a threaded fastener that works itself loose over time due to exposure to chronic vibration, thermal cycling, or other environmental factors presents a serious difficulty. Numerous fastener locking schemes are known for preventing a threaded fastener from working itself out. Some fastener locking schemes include additional locking hardware, such as a locking washer, cotter pin, lock wire, locking cup or lock plate to secure the fastener. Other fastener locking schemes require specialized modification of the surface of the flange or other component secured by the fastener. For example, some locking schemes rely on friction or deformation of the mating surfaces for the locking action while others require a modified opening (e.g., counter-sinked well) into which the fastener head is crimped to lock the fastener. Lock washers, pins, castellated nuts, and lock wire are problematic for securing components inside a nuclear reactor as these components are subjected to long term exposure (e.g., on the order of decades) to flow induced vibration, seismic loads, etc. Loosening or failure of a single fastener in an operating nuclear reactor can require reactor shutdown and unscheduled maintenance.
Similarly, in a UHV system, pump down to operating pressures of around 10−9 Torr or lower typically employs applying a sequence of different pumps (e.g., mechanical, cryogenic, diffusion, ion pumps) in a prescribed sequence over a period of days or weeks. A single fastener failure can require opening the UHV system and consequent unscheduled downtime for pump down on the order of weeks.
The following discloses improved locked fastener arrangements and fastening methods.